I find that insulated clothing and a lighter sleeping bag gives me more utility in the backcountry. It's the system I used all winter. Those pants are a work of art, but I doubt you'll find as much use outside your sleeping bag as you would with a down coat, so keep that in mind.

I have those WM Flash pants and like them a lot.No, they do not have a fly , I like that too because I wear them inside the sleeping bag so I prefer not to have a zip there.In the seat area they have a heavier nylon cover unlike shown in the photos on the website.

I was looking at both the WM and MB ones and instead opted for custom ones from Ben at goosefeet- it actually came out a little cheaper and I was able to customize the materials, the amount of fill (uses 850+) and they are custom sized as well

I already have the MB UL Down pants but have been considering the Flight pants for colder weather. I am put off by the fit I've seen in pics though. Their Unisex sizing seems tailored for women with REALLY big hips relative to waist size. Like for the folks who prefer to drive those electric shopping carts around the Walmart! Are my impressions wrong?

I was in the same boat: MB or WM. I went with WM. It's been a few yrs but it seems I did for the reasons you mentioned. I use them for what you mention too...and they are really nice. However, I made the mistake of getting mediums instead of a large...and they look and feel ridiculous on me. If only I were lucky enough to find someone with a large who wanted a medium........

A while back I was torn between the MB & the WM (Flash) down pants), but I ended up going with the GFG down pants. What I got out of it was a pair of pants that was custom fit, and with my choice of materials. They also have 3.5 oz of down (which is 1.5 oz more than either the WM or the MB-they only have 2 oz), and at only 6.2 oz, lighter than the other options too! As well, I paid $160 for them, which is the same price (or actually lower) as either of the other pairs.

Now, these are with 10D inner/outer shell materials, so they are not as robust as the seat of the WM pants, however, I wear these to sleep in, so I don't need anything super robust. While wearing them around camp, I will just wear my DriDucks rain pants over them to help protect them.

Anyway, I highly recommend them. Here is a write up I did on them a while back:

Also, I disagree with Max about down pants being useless outside of the tent. Having these for standing around camp are a delight, and just as useful (for me) as using them with my sleeping gear. The same goes for my down parka. I never pull out my down parka (MB UL Down Inner) until I get to camp. I don't actually hike in any of my down items, save my BRG down hat, on occasion.

For those of us that don't actually need extra layers on our lower half to hike in, down pants are a great alternative to long underwear. They provide more warmth, and come at a lighter weight penalty. Of course though, this is just my opinion, based on my own personal experience for my neck of the woods... YMMV though...

"I have those WM Flash pants and like them a lot.No, they do not have a fly , I like that too because I wear them inside the sleeping bag so I prefer not to have a zip there.In the seat area they have a heavier nylon cover unlike shown in the photos on the website."

My strategy was going to be to use them to get more hours on the trail. Basically wake up at 5AMish instead of 6AMish when its hella cold and start packing up and cooking while I have my down clothes on.

Though I suspect I might be able to shed the down pants once I leave camp.

Kevin, as I mentioned, I wear mine while at camp and of course while sleeping. This does include when doing camp chores both at night and in the morning. However, when I start packing up, they are the second thing I pack...right after my quilt. I don't hike in mine simply because my lower half is not as bothered by the cold as my upper half, and even if so, once I start hiking they warm up anyway.

If you are warm enough in your clothes at camp you will be far too warm and sweat when you start walking.The commonest "mistake" I see on the trail is people arriving at camp and start peeling off several wet (from sweat) layers.The same people will be cold later on in the evening...Mind you the lowest temp I walk in is around 20f, still the principle applies at -40 too.If you are warm with what you have on at camp at-40 you will be too hot when you start walking.